Polyamide-based paints have a particularly wide range of uses including coatings on wood (furniture, office furniture), on aluminum (prelacquering industry, coatings for roller blinds), on plastic substrates (data processing, audio and video equipment), and as ground coverings (parking, sports grounds).
European Patent EP-0,047,508 relates to applications-of the prelacquering type. This patent describes a coating composition for coating metal objects, making use of the belt lacquering (coil coating) process. The coating composition is characterized in that it contains a vehicle containing a hydroxyl functional group, a blocked polyisocyanate, and a polyamide powder. The coating is subsequently crosslinked at temperatures of between 200 and 260.degree. C., which temperatures are too high to be employed on a rigid PVC section whose distortion threshold lies between 60.degree. C. and 80.degree. C.
Japanese Application 54.64945 No. JP 55157661, published on Dec. 9, 1980, describes a paint that is based on polyamide 6 or 6.6 or 6.10, silicone oil, and a particular urethane prepolymer and is applicable to PVC slide tracks intended for the motor vehicle industry. This coating is employed so as to obtain highly specific characteristics related to the friction coefficient.
French Patent FR 1,469,096 claims a polyurethane/polyamide system intended for ground-covering. The intended objective of this coating is the anti-skid effect.
One of the disadvantages of the PVC window is its white color. Producing colored PVC joinery assumes solving complex technical problems related especially to impact behavior, uniformity of aesthetic qualities and durability, over a wide range of colors, under acceptable economic conditions.
Four techniques which make it possible to impart color to sections are known at present:
coloring in bulk PA1 coextrusion PA1 veneering PA1 painting. PA1 of one (or more) coating(s) with a thickness which may be between 10 and 100 .mu.m and, preferably, between 10 and 40 .mu.m, PA1 of a substrate, preferably of PVC with a variable thickness, in section form. PA1 high weather resistance (resistance to UV, moisture, and the like), PA1 high impact strength even at low temperature (no flaking) PA1 high scratch resistance, PA1 resistance in the Erichsen model 435 test: higher than 15 N. PA1 resistance to wear at the window seals (dubbing during opening and closing), PA1 retention of the tensile resilience of unpainted PVC. The present invention may even improve this tensile resilience after aging because the coating protects the PVC and prevents surface crazing.
Coloring in bulk is difficult because of incompatibilities between some components of the polymers and the pigments, resulting in poor behavior of the material towards the ultraviolet rays. Also, bulk coloring gives rise to high storage costs, since it would be necessary to store and make an inventory of numerous articles in a number of colors.
Coextrusion consists in extruding together the white PVC of the structure and the colored polymethyl methacrylate (PMMA) on the outer parts of the section. While the technique is well-developed and reliable, a number of obstacles arise, essentially of an economic nature. Manufacturing and storage costs are very high.
Veneering is the technique most widely employed at present. It consists in heat-bonding a polymer film onto the sections as they leave the extruder. Colored sections of good quality are thus obtained which have been employed for a number of years without notable failures. However, this technique has two major disadvantages. The impact behavior of veneered PVC is frequently unacceptable in work-site conditions that are often difficult. A significant economic disadvantage is high storage costs. It is necessary to store and make an inventory of numerous articles in a number of colors. Furthermore, the color range is frequently restricted due to storage constraints.